// This long string is placed here due to jsFiddle limitations.
      // It is usually loaded with AJAX.
      var polyline = [
        'hldhx@lnau`BCG_EaC??cFjAwDjF??uBlKMd@}@z@??aC^yk@z_@se@b[wFdE??wFfE}N',
        'fIoGxB_I\\gG}@eHoCyTmPqGaBaHOoD\\??yVrGotA|N??o[N_STiwAtEmHGeHcAkiA}^',
        'aMyBiHOkFNoI`CcVvM??gG^gF_@iJwC??eCcA]OoL}DwFyCaCgCcCwDcGwHsSoX??wI_E',
        'kUFmq@hBiOqBgTwS??iYse@gYq\\cp@ce@{vA}s@csJqaE}{@iRaqE{lBeRoIwd@_T{]_',
        'Ngn@{PmhEwaA{SeF_u@kQuyAw]wQeEgtAsZ}LiCarAkVwI}D??_}RcjEinPspDwSqCgs@',
        'sPua@_OkXaMeT_Nwk@ob@gV}TiYs[uTwXoNmT{Uyb@wNg]{Nqa@oDgNeJu_@_G}YsFw]k',
        'DuZyDmm@i_@uyIJe~@jCg|@nGiv@zUi_BfNqaAvIow@dEed@dCcf@r@qz@Egs@{Acu@mC',
        'um@yIey@gGig@cK_m@aSku@qRil@we@{mAeTej@}Tkz@cLgr@aHko@qOmcEaJw~C{w@ka',
        'i@qBchBq@kmBS{kDnBscBnFu_Dbc@_~QHeU`IuyDrC_}@bByp@fCyoA?qMbD}{AIkeAgB',
        'k_A_A{UsDke@gFej@qH{o@qGgb@qH{`@mMgm@uQus@kL{_@yOmd@ymBgwE}x@ouBwtA__',
        'DuhEgaKuWct@gp@cnBii@mlBa_@}|Asj@qrCg^eaC}L{dAaJ_aAiOyjByH{nAuYu`GsAw',
        'Xyn@ywMyOyqD{_@cfIcDe}@y@aeBJmwA`CkiAbFkhBlTgdDdPyiB`W}xDnSa}DbJyhCrX',
        'itAhT}x@bE}Z_@qW_Kwv@qKaaAiBgXvIm}A~JovAxCqW~WanB`XewBbK{_A`K}fBvAmi@',
        'xBycBeCauBoF}}@qJioAww@gjHaPopA_NurAyJku@uGmi@cDs[eRaiBkQstAsQkcByNma',
        'CsK_uBcJgbEw@gkB_@ypEqDoqSm@eZcDwjBoGw`BoMegBaU_`Ce_@_uBqb@ytBwkFqiT_',
        'fAqfEwe@mfCka@_eC_UmlB}MmaBeWkkDeHwqAoX}~DcBsZmLcxBqOwqE_DkyAuJmrJ\\o',
        '~CfIewG|YibQxBssB?es@qGciA}RorAoVajA_nAodD{[y`AgPqp@mKwr@ms@umEaW{dAm',
        'b@umAw|@ojBwzDaaJsmBwbEgdCsrFqhAihDquAi`Fux@}_Dui@_eB_u@guCuyAuiHukA_',
        'lKszAu|OmaA{wKm}@clHs_A_rEahCssKo\\sgBsSglAqk@yvDcS_wAyTwpBmPc|BwZknF',
        'oFscB_GsaDiZmyMyLgtHgQonHqT{hKaPg}Dqq@m~Hym@c`EuiBudIabB{hF{pWifx@snA',
        'w`GkFyVqf@y~BkoAi}Lel@wtc@}`@oaXi_C}pZsi@eqGsSuqJ|Lqeb@e]kgPcaAu}SkDw',
        'zGhn@gjYh\\qlNZovJieBqja@ed@siO{[ol\\kCmjMe\\isHorCmec@uLebB}EqiBaCg}',
        '@m@qwHrT_vFps@kkI`uAszIrpHuzYxx@e{Crw@kpDhN{wBtQarDy@knFgP_yCu\\wyCwy',
        'A{kHo~@omEoYmoDaEcPiuAosDagD}rO{{AsyEihCayFilLaiUqm@_bAumFo}DgqA_uByi',
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        '|gGahH~s@w}@``Fi~FpnAooC|u@wlEaEedRlYkrPvKerBfYs}Arg@m}AtrCkzElw@gjBb',
        'h@woBhR{gCwGkgCc[wtCuOapAcFoh@uBy[yBgr@c@iq@o@wvEv@sp@`FajBfCaq@fIipA',
        'dy@ewJlUc`ExGuaBdEmbBpBssArAuqBBg}@s@g{AkB{bBif@_bYmC}r@kDgm@sPq_BuJ_',
        's@{X_{AsK_d@eM{d@wVgx@oWcu@??aDmOkNia@wFoSmDyMyCkPiBePwAob@XcQ|@oNdCo',
        'SfFwXhEmOnLi\\lbAulB`X_d@|k@au@bc@oc@bqC}{BhwDgcD`l@ed@??bL{G|a@eTje@',
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        '[upZbuIolI|gFafFzu@iq@nMmJ|OeJn^{Qjh@yQhc@uJ~j@iGdd@kAp~BkBxO{@|QsAfY',
        'gEtYiGd]}Jpd@wRhVoNzNeK`j@ce@vgK}cJnSoSzQkVvUm^rSgc@`Uql@xIq\\vIgg@~k',
        'Dyq[nIir@jNoq@xNwc@fYik@tk@su@neB}uBhqEesFjoGeyHtCoD|D}Ed|@ctAbIuOzqB',
        '_}D~NgY`\\um@v[gm@v{Cw`G`w@o{AdjAwzBh{C}`Gpp@ypAxn@}mAfz@{bBbNia@??jI',
        'ab@`CuOlC}YnAcV`@_^m@aeB}@yk@YuTuBg^uCkZiGk\\yGeY}Lu_@oOsZiTe[uWi[sl@',
        'mo@soAauAsrBgzBqgAglAyd@ig@asAcyAklA}qAwHkGi{@s~@goAmsAyDeEirB_{B}IsJ',
        'uEeFymAssAkdAmhAyTcVkFeEoKiH}l@kp@wg@sj@ku@ey@uh@kj@}EsFmG}Jk^_r@_f@m',
        '~@ym@yjA??a@cFd@kBrCgDbAUnAcBhAyAdk@et@??kF}D??OL'
      ].join('');

      var route = /** @type {ol.geom.LineString} */ (new ol.format.Polyline({
        factor: 1e6
      }).readGeometry(polyline, {
        dataProjection: 'EPSG:4326',
        featureProjection: 'EPSG:3857'
      }));

      var routeCoords = route.getCoordinates();
      var routeLength = routeCoords.length;

      var routeFeature = new ol.Feature({
        type: 'route',
        geometry: route
      });
      var geoMarker = new ol.Feature({
        type: 'geoMarker',
        geometry: new ol.geom.Point(routeCoords[0])
      });
      var startMarker = new ol.Feature({
        type: 'icon',
        geometry: new ol.geom.Point(routeCoords[0])
      });
      var endMarker = new ol.Feature({
        type: 'icon',
        geometry: new ol.geom.Point(routeCoords[routeLength - 1])
      });

      var styles = {
        'route': new ol.style.Style({
          stroke: new ol.style.Stroke({
            width: 6, color: [237, 212, 0, 0.8]
          })
        }),
        'icon': new ol.style.Style({
          image: new ol.style.Icon({
            anchor: [0.5, 1],
            src: 'https://openlayers.org/en/v4.3.1/examples/data/icon.png'
          })
        }),
        'geoMarker': new ol.style.Style({
          image: new ol.style.Circle({
            radius: 7,
            snapToPixel: false,
            fill: new ol.style.Fill({color: 'black'}),
            stroke: new ol.style.Stroke({
              color: 'white', width: 2
            })
          })
        })
      };

      var animating = false;
      var speed, now;
      var speedInput = document.getElementById('speed');
      var startButton = document.getElementById('start-animation');

      var vectorLayer = new ol.layer.Vector({
        source: new ol.source.Vector({
          features: [routeFeature, geoMarker, startMarker, endMarker]
        }),
        style: function(feature) {
          // hide geoMarker if animation is active
          if (animating && feature.get('type') === 'geoMarker') {
            return null;
          }
          return styles[feature.get('type')];
        }
      });

      var center = [-5639523.95, -3501274.52];
      var map = new ol.Map({
        target: document.getElementById('map'),
        loadTilesWhileAnimating: true,
        view: new ol.View({
          center: center,
          zoom: 10,
          minZoom: 2,
          maxZoom: 19
        }),
        layers: [
          new ol.layer.Tile({
            source: new ol.source.OSM()
          }),
          vectorLayer
        ]
      });

      var moveFeature = function(event) {
        var vectorContext = event.vectorContext;
        var frameState = event.frameState;

        if (animating) {
          var elapsedTime = frameState.time - now;
          // here the trick to increase speed is to jump some indexes
          // on lineString coordinates
          var index = Math.round(speed * elapsedTime / 1000);

          if (index >= routeLength) {
            stopAnimation(true);
            return;
          }

          var currentPoint = new ol.geom.Point(routeCoords[index]);
          var feature = new ol.Feature(currentPoint);
          vectorContext.drawFeature(feature, styles.geoMarker);
        }
        // tell OpenLayers to continue the postcompose animation
        map.render();
      };

      function startAnimation() {
        if (animating) {
          stopAnimation(false);
        } else {
          animating = true;
          now = new Date().getTime();
          speed = speedInput.value;
          startButton.textContent = 'Cancel Animation';
          // hide geoMarker
          geoMarker.setStyle(null);
          // just in case you pan somewhere else
          map.getView().setCenter(center);
          map.on('postcompose', moveFeature);
          map.render();
        }
      }


      /**
       * @param {boolean} ended end of animation.
       */
      function stopAnimation(ended) {
        animating = false;
        startButton.textContent = 'Start Animation';

        // if animation cancelled set the marker at the beginning
        var coord = ended ? routeCoords[routeLength - 1] : routeCoords[0];
        /** @type {ol.geom.Point} */ (geoMarker.getGeometry())
            .setCoordinates(coord);
        //remove listener
        map.un('postcompose', moveFeature);
      }

      startButton.addEventListener('click', startAnimation, false);